Thats just how I calculated the power through the 1K at 5V. The 1K is specified in the datasheet, the power is only 25mW if there is a constant 5V accross it so any resistor of 1K should do. Each pin will have a maximum sink current, PICS are quite high so may be worth checking if any one pin needs to supply more than a couple of milliamps (LED Drive for example). Also the device as a whole has a maximum dissipation so just because pins may be able to take 20mA doesn't mean that all 30 I/Os can take 20mA. In a standard application you can probably just replace the PIC with whatever processor you want just matching Input/output and open collectors. And just to re-iterate LOOK IN THE DATASHEET Almost all your questions can probably be answered there. Paul.
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